A specific fused pyrrolocarbazole compound known as 11-isobutyl-2-methyl-8-(2-pyrimidinylamino)-2,5,6,11,12,13-hexahydro-4Hindazolo[5,4-a]pyrrolo[3,4-c]carbazol-4-one is a potent, orally-active TIE-2/VEGF-R 40 inhibitor having anti-tumor and anti-angiogenic activity and is represented by the following formula (I):

This compound is herein-referred to as compound (I). U.S. Pat. No. 7,169,802 describes compound I and utility thereof. It notably discloses a method of preparation of this compound according to scheme 1:

However, the inventors have shown that compound (I) is resulting with poor yields of about 38% and low purity according to such procedure. In particular, it has been shown that the compound of formula (I) thus resulting, contained a high level of the by-product of formula (IV).

This by-product resulting from the elimination of two hydrogen atoms in the indazolyl moiety of the compound of formula (I) and hence from the aromatization of the ring system, turned out to be particularly difficult to separate from compound of formula (I).
Thus, several purification steps, notably by column chromatography, were required to obtain compound (I) with a pharmaceutically acceptable purity, notably of more than 95%, thus even further lowering the yields.
Therefore, there is a need for an improved process for the manufacture of compound (I) from compound (II) that overcomes the drawbacks of the prior art and, in particular, allows to obtain satisfactory yields and purity.